Browsing by Author "Celentano, D. J."

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    A Thermo-metallurgical Model for Laser Surface Engineering Treatment of Nodular Cast Iron
    (2021) Boccardo, A. D.; Catalan, N.; Celentano, D. J.; Ramos-Moore, E.
    Heat treatments are frequently used to modify the microstructure of cast irons according to experimental parameters. Among these, laser surface engineering (LSE) has become relevant for being a highly localized treatment with rapid heating and cooling of the irradiated area resulting in minimal distortion of the workpiece. This work presents and experimentally validates a thermo-metallurgical model able to predict the phase transformations occurring during the LSE treatment of nodular cast iron when it is subjected to different laser beam powers and scanning velocities. For this purpose, an experimental characterization of the thermal history and final microstructure is performed for several operating scenarios. In particular, significant changes in the microstructure can be seen at high powers and low scanning velocity where the matrix is transformed into ledeburite and martensite. The final phase volume fractions predicted by the proposed model along the depth of the sample are compared with the corresponding experimental measurements. The results obtained in the simulation are in good agreement with the experimental measurements. This work highlights the use of our model to be systematically applied for the design and optimization of LSE treatments on cast irons.
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    Analysis of ductile cast iron solidification: numerical simulation and experimental validation
    (TAYLOR & FRANCIS LTD, 2009) Dardati, P. M.; Celentano, D. J.; Godoy, L. A.; Chiarella, A. A.; Schulz, B. J.
    This paper presents an experimental and numerical study of the solidification process of ductile cast iron under slightly hypereutectic conditions. The material thermo-microstructural behaviour is measured in tests performed using standardized cups. Cooling curves at the centre of the cup were recorded, and metallographic studies were carried out to investigate the number and size of graphite nodules at the end of the process. Different models were tested: a model based on a uninodular theory and two models which represent the multi-nodular theory. The cooling curves predicted by these models are in good agreement with the experimental measurements. Some scatter is found, however, in the numerical-experimental comparison for the graphite nodule density at different points of the sample.
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    Computational simulation of microstructure evolution during solidification of ductile cast iron
    (TAYLOR & FRANCIS LTD, 2008) Celentano, D. J.; Dardati, P. M.; Godoy, L. A.; Boeri, R. E.
    This paper presents a thermomicrostructural model for the simulation of the solidification process of an eutectic ductile cast iron. The thermal balance is written at a macroscopic level and takes into account both the structural component being cast and its mould. Models of nucleation and growth represent the evolution of the microstructure, and the microsegregation of silicon is also considered. The resulting formulation is solved using a finite element discretisation of the macrodomain, in which the evolution of the microstructure is taken into account at the Gauss integration points. The numerical results are presented in terms of cooling curves and are compared with available experimental values. Furthermore, the sensitivity of the response with respect to changes in the cooling rate and nucleation parameters are investigated. The agreement between experimental and computational values is acceptable in both quantitative and qualitative aspects. Ways to improve the computational model are suggested.
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    Mechanical behaviour and rupture of normal and pathological human ascending aortic wall
    (2012) Garcia-Herrera, C. M.; Atienza, J. M.; Rojo, F. J.; Claes, E.; Guinea, G. V.; Celentano, D. J.; Garcia-Montero, C.; Burgos, R. L.
    The mechanical properties of aortic wall, both healthy and pathological, are needed in order to develop and improve diagnostic and interventional criteria, and for the development of mechanical models to assess arterial integrity. This study focuses on the mechanical behaviour and rupture conditions of the human ascending aorta and its relationship with age and pathologies. Fresh ascending aortic specimens harvested from 23 healthy donors, 12 patients with bicuspid aortic valve (BAV) and 14 with aneurysm were tensile-tested in vitro under physiological conditions. Tensile strength, stretch at failure and elbow stress were measured. The obtained results showed that age causes a major reduction in the mechanical parameters of healthy ascending aortic tissue, and that no significant differences are found between the mechanical strength of aneurysmal or BAV aortic specimens and the corresponding age-matched control group. The physiological level of the stress in the circumferential direction was also computed to assess the physiological operation range of healthy and diseased ascending aortas. The mean physiological wall stress acting on pathologic aortas was found to be far from rupture, with factors of safety (defined as the ratio of tensile strength to the mean wall stress) larger than six. In contrast, the physiological operation of pathologic vessels lays in the stiff part of the response curve, losing part of its function of damping the pressure waves from the heart.
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    Nodule Evolution of Ductile Cast Iron During Solidification
    (2014) Murcia, S. C.; Ossa, E. A.; Celentano, D. J.
    Ductile cast irons are ferrous alloys in which precipitation of graphite in the form of spherical nodules is embedded in a metal matrix to obtain ductility on the material. Despite the importance of the shape of the nodules, the models proposed to predict the solidification of ductile irons assume a perfect spherical shape during the growing process up to the final solidification of the material, which is proved not to be the case in all castings depending on the processing conditions. The influence of the process parameters on the geometry of the nodules in ductile irons was experimentally evaluated and a model to predict the evolution of nodules during solidification was proposed. The proposed model for growth predicts changes in the nodule count as well as in the nodularity based on different laws for carbon diffusion according to the solid fraction, helping to understand the trends found experimentally. (C) The Minerals, Metals & Materials Society and ASM International 2013